Process of improving the wear properties of a mineral and fatty oil lubricant mixture by radiation



tates No Drawing. Filed Dec. 28, 1959, Ser. No. 862,043 3 Claims. (Cl. 204-162) This invention relates to a process of improving the wear characteristics of a lubricating composition and more particularly to a mineral oil-fatty oil lubricating composition having improved wear characteristics.

The problem of wear in the practice of lubrication is one of the more important considerations, inasmuch as the replacement of operating parts depends upon the extent to which they become worn with use. The amount of wear is greatest when intimate contact occurs between two rubbing surfaces under extreme pressure conditions in the absence of a lubricating film. When such intimate contact between metal surfaces occurs, complete operating failure may result due to seizure of the respective surfaces.

Various means of preventing seizure and improving the wear characteristics of a lubricant have heretofore been suggested. For example, the addition of oiliness and extreme pressure agents to mineral oils have materially improved their wear characteristics. One of the theories behind the use of such agents is that such agents react with one or both of the adjacent metal surfaces to form a chemically bound lubricating film. A chemically bound lubricating film on the surface of a metal is considered by many to be more tenacious than a film which is held in place by mere physical force. Many additives capable of forming such chemically bound lubricating films contain either phosphorus or sulfur. Other compounds capable of forming lubricating films on a metal surfaceinclude the long-chain fatty acids. it is theorized that such acids form metal soaps through the reaction of the acid with an oxide layer on the surface of the metal. While some mineral oils have heretofore been improved in their extreme pressure and wear charatceristics by the addition of a fatty acid, per se, other mineral oils have been improved by the addition of a fatty acid glyceride as found in the fatty oils, i.e., animal, vegetable and fish oils and mixtures thereof.

We have discovered that the wear characteristics of a lubricating composition which comprises a major amount of a mixture of a mineral oil and a fatty oil having an iodine value below about 100 can be substantially improved by subjecting the mixture to ionizing radiation for a time sufiicient for said mixture to absorb at least about 24 and preferably about 50 to about 1000 megareps of radiation while removing heat therefrom at a rate sulficient to maintain the bulk temperature of the oil mixture below its decomposition or vaporization point. As the load under which the lubricating composition is used increases, the amount of ionizing radiation required to give an improved lubricating composition also increases. For example, we have found that the wear characteristics of a lubricating composition comprising a 5050 percent by volume mixture of a highly refined mineral oil and lard oil can be substantially improved when placed at an elevated temperature under a load of kilograms by subjecting the mixture to ionizing radiation for a time sufii- 1 atent 3,ltl0,l Patented Aug. 6, 1963 cient for said mixture to absorb about 24 megareps of radiation. When the load is increased to 20 to 30 kilograms, the lubricating composition must then be irradiated for a time sufiicient to absorb about 50 to about megareps of radiation. As the load is increased above about 30 kilograms, the lubricating composition must be irradiated for a time sufiicient to absorb ionizing radiation in excess of about 100 megareps, preferably about 200 to about 1000 megareps. Thus, the lubricating composition of this invention comprises a major amount of a mixture of a mineral oil and a fatty oil. having an iodine value below about 100, said mixture having been subjected to ionizing radiation for a time suthcient for said mixture to absorb at least about 24 megareps and preferably about 50 to about 1000 megareps of radiation.

A megarep (mrep) is equal to one million reps. A

rep is defined as that dose of any ionizing radiation which produces an energy absorption of 83.8 ergs per gram of material. While the total amount of enregy which must be absorbed by the mixture of mineral and fatty oils to obtain the desired produce is critical, care must be exercised in irradiating the mixture of oils. During irradiation the mixture of oils absorbs the high energy particles which are moving at a high rate of speed. This movement is transferred upon absorption in part into heat. If irradiation is left uncontrolled and is permitted to proceed at too great a rate, the temperature of the oil mixture being treated can be raised to such a level that appreciable decomposition and degradation thereof takes place. Since we have found that these adverse results are produced at elevated temperatures, particularly starting at temperatures of about 200 C., at no time therefore should the bulk temperature of the mixture being irradiated be permitted to rise above about 200 C. Desirably the mixture of oils being irradiated should be maintained during the irradiation period at a temperature as near room temperature as possible so that the changes taking place in the oil mixture are those resulting from irradiation rather than from heat.

Heat resulting from irradiation can be removed from the oil mixture in many ways. One method comprises subjecting the mixtures of oils to ionizing radiation, removing the mixture of oils from the radiation zone as the temperature thereof rises to the levels defined above, reducing the temperature of the oil mixture to a low temperature, such as about 70 to about F., by cycling to a cooling zone, recycling said cooled oil mixture to the radiation zone, and thereafter continuing such a cycling procedure until the oil mixture has absorbed the required amount of energy. Another method, though not preferred, because of the poor heat conductivity of oil mixtures, resides in the use of cooling coils immersed in the oil mixture being irradiated to remove the heat therefrom substantially as fast as the transformation occurs.

The time required for irradiation is extremely important from an economic point of view. When the process is carried out over an extended period of time, it becomes unattractive for commercial use. At the same time, irradiating the oil mixture in too short a time makes it dificult to control the temperature with-in the desired limits. We have found, for example, that an irradiation period per gram of material being irradiated of about 0.1 to about 20 seconds is sufficient to efiect the desired result if we use a 2 million electron volt (2 mev.) Van de Graatf accelerator producing an electron beam at an output of 500 watts. With other power sources, of course, the time will be changed in accordance with the power of the source. Provided heat is removed at a rate sufiicient to prevent substantial decomposition or vaporization of the oil mixture, any irradiation rate can be employed, though extremely high rates may involve technical difliculties.

The mineral oil with which the fatty oil is admixed according to the invention can be any oil having a viscosity within the range of the common lubricating oils. The mineral :oil, for example, can be either a refined or semi-refined paraflinic, naphthenic or asphalt base oil. If desired, a blend of :oils of suitable viscosity can be employed instead of a single oil, by means of which any desired viscosity may be secured. The problem of excessive wear is frequently encountered in heavy machinery where an oil having a viscosity in excess of about 150 SUS at 100 F. is employed. Therefore, this invention has particular application with respect to improving the wear characteristics of a mineral oil having a viscosity above about 150 to 200 SUS at 100 F. The mineral oil content of the compositions of this invention will vary depending upon the ultimate use for which the composition is intended. In general, however, the mineral oil content comprises about 50 to about 90 percent by volume of the total composition. The particular mineral lubricating oil as well as the exact amount of such oil employed therefore depends upon the characteristics desired in the final composition.

The fatty oil component of the compositions of the invention is preferably a non-drying oil. Non-drying fatty oils are preferred because they show very little tendency to gum or thicken when exposed to air. Such non-drying fatty oils generally have iodine values below about 100. Examples of fatty oils having iodine values below 100 are castor oil, olive oil, palm oil, lard oil, neats-foot oil and sperm oil. Fatty oils having an iodine value above about 100 can be used in lubricating compositions of the invention provided such oils are first hydrogenated to such an extent that the hydrogenated oil has an iodine value below about 100. Thus, when we refer to a fatty oil having an iodine value below about 100, it will be understood that we mean a fatty oil whose initial iodine value is below 100 as well as a fatty oil whose initial iodine value is above 100 but which has been bydrogenated to such an extent that its ultimate iodine value is below about 100. Examples of fatty oils having initial iodine values above about 100 but which can be used in compositions of our invention after being hydrogenated to give iodine values below about 100 are cod oil, herring oil, salmon oil, sardine oil, whale oil, menhaden oil, seal oil, soya bean oil, candlenut oil, corn oil, cottonseed oil, peanut oil, and the like. Of the fatty oils having an initial iodine value below about 100, we prefer lard oil because of its availability. Of the fatty oils having an iodine value prior to hydrogenation above about 100, we prefer menhaden oil because of its relative cheapness. As between lard oil and menhaden oil, We prefer lard oil because it requires no hydrogenation prior to use in the compositions of our invention. The fatty oil content of the compositions of the invention depends upon the Ulljn mate use for which the composition is intended. In general, however, the fatty oil content comprises about to about 50 percent by volume of the total composition.

The irradiated oil mixture produced according to this invention may be used, per se, as a lubricant, or it may be used as an additive to improve conventional lubricants in any desired proportion. When used as such or as an additive, a 50-50 mixture of mineral and fatty oils can be employed. In instances where the mineral oil comprises (from 60 to 90 percent by volume of the lubricating composition, it is advantageous from an economic standpoint to irradiate a mineral oil-fatty oil mixture containing at least about 50 percent and preferably 4 about 60 to about percent by volume of fatty oil, thereafter admixing the irradiated mixture with unirradiated mineral oil to give the desired ratio of mineral oil to fatty oil.

The lubricating composition of our invention can contain minor amounts of addition agents normally added to lubricating oils for a specific purpose such as an antioxidant, dispersant, detergengpour point depressant, corrosion inhibitor, viscosity index improver, anti-foamant, and the like. The lubricating composition can also contain other oiliness and extreme pressure agents to further enhance the wear characteristics when desired.

We do not wish to limit this invention to any particular method of radiation inasmuch as the effects of radiation on mixtures of mineral and fatty oils are essentially the same insofar as anti-wear characteristics are concerned regardless of the radiation source. Ionizing radiations can be obtained, for example, by using radio isotopes, nuclear reactors or high energy particle accelerators. Examples of radio isotopes which can be used are cobalt 60 for gamma and strontium 90 for beta. Operating nuclear reactors of intermediate or full power size can be used as a source for either gamma rays or neutrons or both. Particle accelerator-s such as the cyclotron, bevatron, synchrotron, Van de Graaff, or X-ray machines can also be used.

In effecting irradiation of the mixture of oils, the oils can be introduced into a Well in a nuclear reactor 01' through a tube which traverses the reactor. In some instances where it is desirable to expose the oil mixture to fast or high energy neutrons only, and in the substantial absence of beta and gamma radiation, the irradiation can be conducted outside of the reactor using a oollimated beam of fast neutrons. Such a collimated beam of fast neutrons can be obtained, for example, as described in U.S. Patent No. 2,708,656 to Enrico Fermi and Leo Szilard, by inserting a hollow shaft or tube into the central portion of the reactor. Gamma rays can be screened from the fast neutron beam by means of a sheet of bismuth metal extending across the path of the beam.

A neutron-free radiation source can be obtained directly from a homogeneous reactor by separating the radio-active fission gases, xenon and krypton, from the reactor core by conventional or modified gas-liquid separating means. A continuous supply of the radioactive fission gases could be obtained from such a reactor. The fission gases have .a very high intensity of beta and gamma radiation but a very short half life. These gases possess about one percent of the total fission energy. The gases are chemically inert and therefore would not form undesired side reaction products.

High voltage apparatus capable of producing a beam of high energy electrons is described in U.S. Patent No. 2,144,518, which issued on January 17, 1939, to W. F. Westendrop and was assigned to General Electric Company. The apparatus described in the patent to W. F. Westendrop comprises, in general, a resonant system having an open-magnetic circuit inductance coil positioned within a tank and energized by a source of alternating voltage to generate high voltage across its extremities. At the upper end of a sealed-off, evacuated, tubular envelope is located a source of electrons which is maintained at a potential of the upper extremity of the inductance coil whereby a pulse of electrons is accelerated down the tubular envelope once during each cycle of the energizing voltage when the upper extremity of the inductance coil is at a negative potential with respect to the lower end. Further details of the apparatus are given in the patent to W. F. Westendrop and in Electronics, volume 16, pages 128 to 133 (1944).

A method of delivering the ionizing energy of a concentrated beam of high energy electrons to matter to be irradiated with a minimum of secondary or side chemical efiects due to low energy ionized particles, as described in U.S. Patent No. 2,737,593, issued to D. M. Robinson on March 6, 1956, and assignedto High Voltage Engineering Corporation, comprises focusing a concentrated beam of high energy electrons into the form of a thin sheet and causing the matter to be irradiated to travel through said sheet transversely thereto.

Apparatus for irradiating various materials by a continuous beam of high-voltage electrons, as described in Us. Patent No. 2,680,814, issued to D. M. Robinson on June 8, 1954, and assigned to High Voltage Engineering Corporation, comprises discharging the material being irradiated at a high pressure and a high velocity directly into the high-voltage electron beam, whether or not the electron beam is focused into the shape of a thin sheet.

Still other methods and apparatus for effecting irradiation with high energy electrons are described in U.S. Patents 2,602,751 and 2,729,748, issued to D. M. Robinson on July 8, 1952, and January 3, 1956, respectively, and U8. Patent No. 2,680,815, issued to E. A. Burrill on June '8, 1954, all of these patents being assigned to High Voltage Engineering Corporation. We wish to reiterate, however, that inasmuch as the present invention does not reside in any particular method of supplying or efiecting ionizing radiation, other means of radiation, whether through the use of high energy electrons, neutrons or radio isotopes, can be employed in providing a lubricating composition having improved wear characteristics in accordance with the invention without departing from the scope thereof.

While we are not certain as to the exact nature of the changes which take place when a mixture of mineral and fatty oils is subjected to ionizing radiation, we believe that some interaction occurs between the two oils. A 50-50 mixture of a naphthenic mineral oil and lard oil, for example, changes from a viscosity of about 258 SUS at 100 F. to a viscosity of about 328 SUS at 100 F. when irradiated for a time sufficient to absorb about 100 megareps of radiation.

In order to illustrate the improved wear characteristics of the composition of the invention, comparative tests were made in the Precison-Shell Four Ball Wear Test machine. This machine is designed so that three balls are fixed in a horizontal plane in a cup while a fourth ball which is movable is rotated in a fixed position contacting the other three balls to form an equilateral tetrahedron. The test cup is placed on a stage which can move vertically to facilitate loading. The stage rests on a calibrated fulcrum so that specific weights may be applied to force the three balls in the cup to contact the rotating fourth ball at a predetermined pressure. The cup holding the three balls also contains the test lubricant at a level of 2 mm. above the balls, thus assuring an adequate supply of lubricant at the contact points. A fixed oil temperature is maintained by a relay system connected to a thermocouple in the cup and a heater in the stage. The fourth ball can be rotated from a motor drive at 600, 1200, or 1800 r.p.m. Each test is run with new steel balls.

A test is run on a lubricant at a specific load, temperature, speed, and time. Lubricating properties are evaluated from the diameter of the scars on the three balls. A more complete description of the machine and test method are given in the Naval Research Laboratory Report entitled A Study of the Four Ball Wear Machine, by W. C. Clinton, NRL Report 3709, September In illustrating the improved lubricating characteristics of a composition of the invention, the movable ball was rotated at 1800 rpm. under lever loads of to kilograms for one hour with the test lubricant being maintained at 110 C. The lubricants which were tested consisted of an unit-radiated 50-50 mixture of lard oil and a naphthenic mineral oil and the same 50-50 mixture subjected to ionizing radiation dosages of 24, 50* and 100 megareps. Irradiation was effected at room temperature with high energy electrons in a 2 million electron volt (2 mev.) Van de Graatf machine built by High Voltage Engineering Corporation, of Cambridge, Massachusetts. The advantageous wear properties of the irradiated oil mixture as compared with the unirradiated mixture are illustrated by the data set forth in Table 1.

TABLE 1 Irradiation of a 50-50 Mixture of Lard Oil and a Naphthenic Mineral Oil Irradiation dosage, mrep 0 24 50 'It is apparent from the data tabulated above that irradiation of a mixture of lard oil and mineral oil at 24 megareps has a very beneficial eifect in reducing the amount of wear at a load of 10 kilograms. It Will be noted further that to obtain improvement in wear at 20 to 30 kilograms, the mixture of lard oil and mineral oil must be irradiated for .a time sufiicient to absorb at least 50 megareps of radiation. At loads above about 30 kilograms, irradiation in excess of 100 megareps is required.

The results of further tests on an unirradiated 50-50 mixture of lard oil and a naphthenic mineral oil and the same 50-5'0 mixture subjected to ionizing radiation dosages of 100 and 200 megareps are set torth in Table 2. Irradiation in this instance was effected at room temperature with high energy electrons in a 3 mev. Van de Graatf machine.

The data summarized in Table 2 show that improvement in wear at loads of 10 to 20 kilograms can be realized when the oil mixture is irradiated for a time sufiicient to absorb 100 megareps of radiation. At a load of 30 kilograms, improved wear characteristics were obtained at an irradiation dosage of 200 megareps.

The physical characteristics of two improved compositions of the invention comprising .a 5 0-5 0 mixture of lard oil and mineral oil which has been irradiated .for a time sutficient to absorb about 100 megareps and about 200 megareps of radiation as compared with the mixture prior to irradiation are shown by the inspection data in Table 3.

While our invention has been described above with reference to various specific examples and embodiments,

it will be understood that the invention is not limited to such illustrative examples and embodiments, and may be variously practiced within the scope of the claims hereinafter made.

We claim:

1. A process of improving the wear characteristics of a lubricating com-position consisting essentially of a mixture of about 50 to about 90 percent by volume of a mineral oil and about 10 to about 50 percent by volume of a fatty oil having an iodine value below about 100, which comprises subjecting said mixture to ionizing radiation for a time :suflicient for said mixture to absorb at least about 24 megareps of radiation.

2. A process of improving the wear chanacteristics of a lubricating composition consisting essentially of a mixture of about 50 to about 90 percent by volume of a mineral oil and about 10 to about 50 percent by volume of a fatty oil having an iodine value below about 100, which comprises subjecting said mixture to ionizing radiation for a time sufiicient for said mixture to absorb about 24 to about 1000 megareps of radiation.

3. A process of improving the wear characteristics of a lubricating composition consisting essentially of a mix- 8 ture of about to about percent by volume of a mineral oil and about 10 to about 50 percent by volume of lard oil, which comprises subjecting said mixture to ionizing radiation for \a time sufficient ior said mixture to absorb about 24 to about 1000 megareps of radiation.

References Cited in the file of this patent UNITED STATES PATENTS 2,138,868 Liberthson Dec. 6, 1938 2,170,665 Russell Aug. 22, 1939 2,178,769 Wiezevich Nov. 7, 1939 2,350,330 Remy June 6, 1944 OTHER REFERENCES Mincher: Summary of Available Data on Radiation Damage to Various Non-Metallic Materials, KAPL-73l, Apr. 2, 1952, by Knolls Atomic Power Laboratory, General Elecrtic Co., Schenectady, N.Y., pp. 37.

Bastian: Metalworking Lubricants, 1951, McGraw- Hill Book Co., Inc, pp. 11 and 14.

Otto: Improving the Oiliness of Lubricants, The Petroleum Engineer, January 1931, pp. 112 and 115. 

1. A PROCESS OF IMPROVING THE WEAR CHARACTERITICS OF A LUBRICATING COMPOSITION CONSISTING ESSENTIALLY OF A MIXTURE OF ABOUT 50 TO ABOUT 90 PERCENT BY VOLUME OF A MINERAL OIL AND ABOUT 10 TO ABOUT 50 PERCENT BY VOLUME OF A FATTY OIL HAVING AN IODINE VALUE BELOW ABOUT 100, WHICH COMPRISES SUBJECTING SAID MIXTURE TO IONIZING RADIATION FOR A TIME SUFFICIENT FOR SAID MIXTURE TO ABSORB AT LEAST ABOUT 24 MEGRAREPS OF RADIATION. 